Modern aircraft contain visual display systems that provide flight crews with substantial amounts of important operational and situational awareness information about the environment outside the aircraft, such as terrain. In fact, multi-functional aircraft displays that provide flight crews with computer-enhanced, three-dimensional perspective images of terrain (e.g., especially during conditions of low visibility) are known. One approach used to enhance terrain imagery in existing multi-functional aircraft displays is to combine high resolution, computer-generated terrain image data derived from onboard databases (e.g., synthetic vision systems) with enhanced, real-time terrain image data derived from onboard vision sensor systems (e.g., Forward Looking Infrared/FLIR sensors, active and passive radar devices, etc.). However, a major drawback of this approach is that significant data integrity issues exist with the computer-generated terrain information derived from the onboard databases, and significant non-intuitive imaging issues exist with the real-time terrain information derived from the vision sensor systems. Also, similar issues may arise in other applications. For example, data integrity and imaging issues can arise with the use of synthetic vision displays for Unmanned Aerial Vehicle (UAV) operations, and high-fidelity flight training simulators using flight worthy data sources where certain targets or objects are mapped with higher accuracy than the underlying terrain. As a result of these problems, visual display disparities and operator errors can occur.
For example, in today's aircraft displays, high resolution terrain data has to be provided on a continuous basis to an onboard graphics display processor, in order for the processor to produce steady, three-dimensional perspective view images of the terrain for critical flight applications. However, since terrain data for aircraft applications typically covers the entire globe on a continuous basis, such an onboard database would contain an enormous amount of terrain data. Thus, it would be an almost impossible task to physically verify all of the data points in such a database for critical flight applications. As such, other techniques are required to correct and augment this data, and especially during the operational phases where the terrain information is important for flight applications, such as during take-offs and landings or near terrain-challenged areas. Additionally, the techniques used for data correction and augmentation need to lead to information presented to flight crews in correct and natural formats so as not to introduce additional confusion factors during the critical phases of flight operations. Generally, real-time data correction and augmentation techniques need to be performed in those applications where the terrain information displayed has more impact for flight operations, and where other data from more accurate sources (e.g., localized databases, real-time sensors, uplinks from ground-based databases, etc.) are available.
Another significant problem with the use of high resolution terrain data for these perspective view display applications is that they place a heavy load on the processor involved, and therefore, certain data computation techniques (e.g., simple- or continuous-level of detail computation techniques) have to be used in order to reduce the computational workload. Additionally, the terrain data is also decompressed and dynamically displayed. Consequently, using the existing data computation techniques, whenever a large patch of terrain data is loaded for pre-processing during the initialization phase (e.g., immediately after the terrain display application is turned on), the processing system experiences a significant latency period and a corresponding delay before that data can be displayed. Similarly, using existing data computation techniques, if the processing system attempts to load such terrain data in real-time, then significant discontinuities and instabilities can occur with the display of the data derived from regions close to the borders of previously loaded data. As such, these data integrity and processing problems impose significant data storage and processing limitations on existing onboard aircraft display systems, which significantly limit the usefulness of displays for flight critical applications. Since it is impractical to completely verify all of the data stored in the database, a viable data computation technique is needed that will enable a processor to produce steady, perspective view images of terrain information for critical flight applications, whereby the terrain information is derived from the fusion of high resolution terrain data retrieved from a database, with real-time data received from one or more vision sensor systems, an onboard database having higher data precision in localized areas, one or more radar sensors, or precision data uplink from one or more ground stations. In any event, an example of the above-described data computation problem is illustrated by FIG. 1, which depicts an existing computer-generated aircraft display.
Referring to FIG. 1, display 100 represents a conventional onboard electronic display, such as, for example, a Primary Flight Display (PFD) and/or a Heads-Down Display (HDD). Display 100 shows, among other things, computer-generated symbols representing a zero pitch reference line 102, a flight path marker (also known as a flight path vector, or velocity vector) 104, an airspeed scale or tape 106, an altitude scale or tape 108, and natural terrain (e.g., identified generally as element 110). Essentially, as an aircraft approaches an airport (e.g., man-made terrain feature) for landing, the pilot locates an intended runway (e.g., also man-made terrain feature), and aims the aircraft in the direction of the runway. The pilot aims the aircraft at the runway by controlling the aircraft's movement, which typically results in the runway remaining in the close vicinity of the flight path marker symbol 104. However, as illustrated by the example shown in FIG. 1, a runway symbol is not being displayed, although it may be assumed that the arrow 112 identifies the known location of a runway relative to this view. In this case, the elevation of the terrain data that produces the computer-generated three-dimensional image (e.g., of natural terrain 110) is slightly higher than the elevation of the runway data (e.g., for the man-made terrain/runway at location 112). Thus, due to the aforementioned problems with the existing data computation techniques used, the symbol for the runway known to be at location 112 is obscured on conventional display 100. As such, this loss of visual contact of such critical runway/terrain information by a pilot (e.g., especially in the vicinity of that airport) decreases the effectiveness, accuracy and safety of the flight decisions being made, and thus increases the possibility that dangerous flight management, navigation or control errors can occur. Therefore, it would be advantageous to have a system and method that enhances computer-generated terrain images on an electronic display, such as, for example, a PFD, HDD, or similar electronic aircraft display. As described in detail below, the present invention provides such a system and method, which resolves the terrain data integrity problems, data computation problems, and terrain visibility problems encountered with existing electronic aircraft displays.